Antennas are used in a prodigious assortment of wireless communication applications. For example, portable wireless communications devices may use a straight conductor or an inductively loaded conductor as an antenna that extends from a housing of the communications device. The conductor may form a whip antenna which is subject to breakage from abusive treatment, or even ordinary wear and tear of wireless users. If the whip antenna is broken, bent or otherwise damaged, communications can be disrupted or become less reliable than would otherwise be possible. Further, the size of the protruding whip antenna may increase the overall size of the mobile wireless communications device.
To prevent damage to whip antennas and other external antennas that protrude from the housing of the wireless communications device, some manufacturers have introduced internal antennas that are housed within a housing of a mobile communications device. For example, an antenna may be fabricated as a cavity-backed aperture antenna within the housing of a wireless communications device. However, the nominal depth of the cavity-backed aperture antenna is approximately one-quarter wavelength of the frequency of operation. If the depth of the cavity-backed aperture antenna could be reduced from the nominal value of approximately one-quarter wavelength, the size of the mobile communications device could be reduced accordingly, or additional electronics and functionality could be introduced in the same size of an electronic device. Thus, a need exists for an integral aperture antenna that has a thickness of or depth of less than one-quarter wavelength at the desired frequency of operation.
Another problem with the cavity-backed aperture antenna or other integrated antennas is that the surrounding electronics in the mobile communications device, or even the hand of a user of the communications device, can detune the antenna and degrade the radiation efficiency of the antenna. The surrounding electronics or body of the user may distort the antenna pattern from theoretically predicted results so as to produce unreliable communications that differ from what would be expected under ideal circumstances. Thus, a need exists for an antenna that reduces the effect of surrounding electrical components and the bodies of users upon the performance of an antenna integrated into a mobile communications device.
Although aperture antennas may be used for mobile communications devices, aperture antennas may be employed in a variety of environments such as antennas for vehicles, base station antennas, tower-mounted antennas for wireless infrastructure, or the like. If a whip antenna or half dipole antenna is mounted on an exterior of a vehicle it may impair the aerodynamic performance of the vehicle by increasing aerodynamic drag and reducing fuel mileage. Further, a protruding antenna on a vehicle is subject to damage or breakage from wind gusts, vandalism, and car washes. Thus, a need exists for embedded, flush-mounted or other compact antennas for integration into a vehicle.
If aperture antennas or cavity-backed aperture antennas are used for wireless infrastructure applications, the antennas may be larger than desired for reduction of wind-loading, ease of installation and enhancement of aesthetic appearance. Space limitations on cramped towers or other structures tend to increase the desirability for smallest profile antennas with comparable performance to larger antennas. Thus, a general need exists to provide a compact antenna that provides adequate radiation performance while achieving aesthetic or space-saving goals.